In a blood test, a blood testing tool having a porous material to be impregnated with blood conventionally has been used for various purposes.
According to such a blood testing tool, the test can be carried out, for example, by impregnating the porous material with blood so that a component in the blood reacts with a reagent that has been provided in the porous material beforehand and then measuring the result directly by an optical or electrochemical method. Alternatively, the blood may be extracted from the porous material and recovered, and the test may be carried out on this as a sample.
Such a blood testing tool has been used in general clinical tests or the like. In recent years, the suitability of such a blood testing tool has been studied for use in remote clinical testing systems. Indeed, it is actually used in certain remote clinical testing systems. In such a remote clinical testing system, a patient collects blood by himself at home, and the blood testing tool is impregnated with the blood. This then is dried, and the blood testing tool then is mailed to a test institute such as a hospital for testing. The system allows the patient who mailed the blood to be informed of the test result by mail or the like without visiting the hospital. In addition, because the patient can visit the hospital or the like for treatment after receiving the test result, the necessity of collecting blood at the hospital is eliminated, which reduces the labors of both the hospital stuff and the patient.
When the test item is a component contained in blood serum or blood plasma, such as blood glucose or the like, it is necessary to separate blood cells from blood in the blood testing tool. A conventional blood testing tool generally is a laminate in which a blood cell separator such as a glass filter or the like is laminated on a recovery porous material into which blood serum or blood plasma penetrates. In such a blood testing tool, when blood is supplied to the upper surface of the blood cell separator, the blood moves in the thickness direction inside the blood cell separator, during which blood cells in the blood are retained in the blood cell separator so that only blood serum or blood plasma passes through the blood cell separator. The blood serum or blood plasma having passed through the blood cell separator penetrates into the recovery porous material as the lower layer of the laminate and is retained therein (hereinafter, such blood cell separation is referred to as “vertical separation”). In such vertical separation, a surface area involved in the separation is greater than in transverse separation to be described later. Thus, the blood serum or blood plasma having passed through the separator penetrates, thereby allowing an excellent recovery rate to be achieved.
However, a laminate-type blood testing tool employing such vertical separation has a problem in that the blood cells retained in the blood cell separator may hemolyze at the interface between the blood cell separator and the recovery porous material. If such hemolysis occurs, components that flowed out from the blood cells due to the hemolysis penetrate into the recovery porous material as the lower layer of the laminate and interfere with the measurement.
In order to solve the problem caused in the vertical separation, a blood testing tool has been developed in which blood moves in a direction parallel to the surface (which is a transverse direction and hereinafter, referred to simply as a “surface direction”) rather than in a thickness direction (a vertical direction) to separate blood cells (hereinafter, such blood cell separation is referred to as “transverse separation”, which is disclosed in JP 2001-188066 A etc.). The transverse separation can be carried out, for example, in a blood testing tool including an asymmetric porous membrane with pores whose sizes vary in the surface direction. For example, when blood is supplied to the asymmetric porous membrane from the side having larger pores, the blood moves from the upstream with larger pores to the downstream with smaller pores along the surface direction by the capillary phenomenon. When the blood cells reach the portion with pores through which they cannot pass, they are retained therein so that only blood serum or blood plasma penetrates further downstream. Thus, in this blood testing tool, since blood cells are separated during the movement in the surface direction due to the variation in pore sizes, the above-described problem of the hemolysis of blood cells at the interface is not caused. Therefore, it is possible to recover only blood serum or blood plasma containing no components of blood cells.